1. Field of the Invention
This invention relates to data transmission. More specifically, the invention relates to the streaming of media content in a Multimedia Messaging Service.
2. Description of the Prior Art
In mobile communications networks, the term Multimedia Messaging Service (MMS) is commonly used to describe a new approach for transmitting messages having multimedia content. The Multimedia Messaging Service allows messaging between different mobile users and/or between mobile users and the Internet. There is an already agreed solution for providing an MMS in 3rd Generation mobile communication networks and its features are described in 3rd Generation Partnership Project (3GPP) Technical Specification (TS) 23.140, V.4.1.0 “Multimedia Messaging Service (MMS), Functional Description, Stage 2 (Release 4, 2000-12)”. The Multimedia Messaging Service proposed in 3GPP TS 23.140, release 4 employs a store-and-forward approach to message delivery. Multimedia messages are constructed in such a way that the media content, information necessary to describe the media content and addressing information, identifying the intended receiver of the message, are encapsulated together. The multimedia message is then sent from a sending MMS user agent to a Multimedia Messaging Service Center MMSC, which in turn notifies the intended receiver (recipient MMS user agent) about the message. Later on, the multimedia message is downloaded by the recipient MMS user agent terminal as a whole and only presented to the user once downloaded and stored in the recipient MMS user agent.
Next, the structure and operation of a typical MMS system will be described with reference to FIGS. 1, 2 and 3.
FIG. 1 shows an overview of MMS system elements according to 3GPP TS 23.140. The system comprises the following items:                a plurality of MMS user agents (UAs) 110, each of which is capable of transmitting and receiving multimedia messages;        a roaming MMS user agent 127;        Access networks 122, 124 and 126 of different types including:                    A second generation mobile telecommunications network 122 such as a GSM phase 2 network;            A third generation mobile telecommunications network 124 such as a Universal Mobile Telecommunications System (UMTS); and            A mobile access network 126, for example a wireless-LAN network.                        The Internet (or another Internet Protocol (IP)-network) 130, having an external server 134, such as an e-mail server, and a wired E-mail client 132;        A Multimedia Messaging Service relay 142 and an MMS server 144 which, in this example, are integrated into a single unit, referred to as a Multimedia Messaging Service Centre (MMSC) 140, but which can alternatively be implemented as separate or distributed entities;        A message store 150 in connection with the MMS server 144; and        User databases 160 comprising, for example, user subscription and addressing information.        
The collective term Multimedia Messaging Service Environment (MMSE) is used to describe those functional elements that operate together to implement a multimedia messaging service. In FIG. 1, an MMSE is formed by the elements within the oval outlined region.
Referring in further detail to FIG. 1, each MMS user agent 110 connects to the MMS relay 142 through its access network 122, 124. The roaming MMS user agent 127 connects to the MMS relay 142 through the mobile access network 126 and via the Internet 130. The MMS relay is connected to the MMS server 144 and to the user databases 160. Furthermore, the external server 134 and the wired E-mail client 132 are connected to the Internet 130.
FIG. 2 shows an overview of interworking between different MMSE's according to 3GPP TS 23.140. The communication of multimedia messages takes place between user agents 110A (sender) and 110B (recipient) which reside in two different Multimedia Messaging Service Environments. For simplicity and clarity, the two Multimedia Messaging Service Environments, MMSE A and MMSE B, are each shown to comprise a single MMS relay, linked to a single MMS server, thus forming two MMSC's 214 and 224. It should be appreciated that in a practical MMSE, the number of MMS relays and servers may be, and typically will be, greater than this. MMSE A and MMSE B may, for example, have different operators, different geographical locations or coverage areas and/or differ in terms of their technical characteristics and capabilities. Furthermore, in the situation where a particular MMSE comprises more than one MMS relay, the method according to the invention can also be applied within the MMSE.
In the example shown in FIG. 2, both MMS user agents 110A and 110B are depicted as devices that communicate with their respective MMSE 210, 220 via a radio communication network 212, 222. However, it should be appreciated that either MMSE user agent A or MMSE user agent B, or both of them, could reside in a fixed line network (not shown).
In connection with FIG. 2, it is assumed that MMS user agent A 110A, which has subscribed to the multimedia messaging service provided in Multimedia Messaging Service Environment A 210, wishes to send some media content to MMS user agent B 110B, which has a subscription to the multimedia messaging service provided in MMSE B 220. In general, the content of a multimedia message can comprise a variety of components, some of which are suitable for streaming and other components which are not typically suitable for streaming, such as text or still images. In the following example, which describes the creation, transmission and retrieval of a multimedia message, it is assumed that all the components of the message are non-streamable content types. The current provisions for streaming download of multimedia message components provided by 3GPP TS 23.140 will then be considered separately.
Referring once more to FIG. 2, when initiating the communication of a multimedia message to MMS user agent B, MMS user agent A first selects the media content to be transmitted. For example, the media content may take the form of a still image and some associated text, stored in the memory of user agent A. The image may have been recorded, for example, using a camera, and still image encoding equipment built into user agent A. Alternatively, the image and text may already have been downloaded from another source to user agent A. In either case, user agent A encapsulates the media content as a multimedia message, comprising the media content itself, information necessary to describe the media content and addressing information, identifying the intended recipient of the message. MMS user agent A then sends the message to MMS relay A through radio network A 212.
On receiving the multimedia message, MMS relay A determines, from the addressing information included with the message, that the intended recipient is not a user agent of MMSE A, but a user agent of MMS relay B and forwards the multimedia message to MMS relay B. Routing of the multimedia message to the correct MMS relay, i.e. that responsible for MMS user agent B is achieved, for example, using standardised mechanisms provided for in the existing 3GPP multimedia messaging solution. On receiving the multimedia message, MMS relay B stores the media content in MMS server B and sends a notification to the intended recipient, MMS user agent B, thereby indicating that a multimedia message has arrived and its content is available to be downloaded from MMS relay B. In response to receiving the notification, MMS user Agent B retrieves the media content from (via) the MMS relay B. The retrieval of the media content is initiated by signalling with MMS relay B.
FIG. 3 illustrates the process of notification and multimedia message retrieval in more detail. Specifically, FIG. 3 shows the flow of messages that takes place when MMS relay B receives an MMS message intended for recipient MMS user agent B. MMS relay B receives the MMS message, stores it in MMS server B, and then informs MMS user agent B of the arrival of the message using an MMS notification message 310 (MM1_notifcation.REQ in 3GPP TS 23.140).
Next, the MMS user agent B responds with an MMS notification response 320 (MM1_notifcation.RES in 3GPP TS 23.140) to acknowledge receipt of the MMS notification 310.
Having received the MMS notification message 310, MMS user agent B is aware that a multimedia message is available for retrieval and may initiate a process to download the message. This may be done substantially as soon as the notification message is received, or may be performed at some later time. When MMS user agent B desires to start downloading the MMS message, the agent sends an MMS retrieve request 330 (MM1_retrieve.REQ) to MMSC B 224. MMSC B 224 responds by retrieving the multimedia message from MMS server B and sends an MMS retrieve response 340 (MM1_retrieve.RES in 3GPP TS 23.140) to MMS user agent B. In the case of a multimedia message that comprises only non-streamable media components, as considered in this example, the MMS retrieve response message carries the actual multimedia message components to be downloaded. After receipt of the entire multimedia message, the MMS user agent B sends an MMS acknowledgement 350 (acknowledging the receipt of the entire multimedia message) to the MMS relay B.
As mentioned earlier, some media components may be suitable for downloading by streaming. The term “streaming” is generally used to describe the presentation of media content, for example an audio or video clip, or a combination of different media types, in a continuous way while the content is being transmitted to a recipient over a data network. A “stream” can be a flow of data enabling the recipient to present some continuous flow of information such as motion pictures (i.e. video), voice or music. In a typical video stream, some 10 to 20 video frames are transmitted per second. In practice, streaming can be either live (real-time) or performed in an on-demand fashion. The term “live streaming” describes the creation of a media stream from a live source, for example a stream of digital images produced by a video camera, while the term “on-demand streaming” describes the creation of a media stream from, for example, a file stored on a server.
The application of streaming in mobile networks looks very promising, especially considering the fact that mobile terminals typically have limited multimedia playing resources such as memory and processing power. In general, the adoption of a streaming approach to media download and presentation has the potential to reduce the amount of available memory required by mobile terminals
Recently, interest has also arisen in the incorporation of streaming into the proposed 3rd generation multimedia messaging service. However, as mentioned earlier, the MMS service is based on the encapsulation of media content, message description and addressing information into a single message. This kind of encapsulation is incompatible with the streaming of media content and therefore certain modifications to the MMS service recommendations are necessary in order to accommodate the streaming download of media content. 3GPP TS 23.140, release 4 allows a streaming session to be established between a recipient user agent and a recipient MMS relay, but requires that the notification message sent from the recipient MMS relay to the recipient MMS user agent be modified to a certain extent.
According to the recommendation, if a recipient MMS relay, such as MMS relay B described in the above example, receives a multimedia message containing streamable media content, the relay forms a modified MMS notification message and sends it to the intended recipient user agent to notify it about the streamable media components. The modified notification message contains information necessary to initialise a streaming session between the recipient MMS user agent and an MMS server that has access to the streamable media components.
Thus, according to 3GPP TS 23.140, release 4, the standard MMS notification message, used to inform an intended recipient user agent that a multimedia message is available for download, must be modified in such a way as to provide particulars of a streamable media component to be downloaded. This enables the recipient user agent to establish a streaming session to download the media component.
However, despite this modification, there is still no mechanism available in the MMS specification to enable the downloading of both streamable and non-streamable media components in a consistent manner. There is a need for such a capability, because of the usefulness of receiving both non-streamable media components, such as still pictures and text or program applets together with streamable media components such as sound, voice or video streams.